Anisaldehyde production and aryl-alcohol oxidase and dehydrogenase activities in ligninolytic fungi of the genus Pleurotus

Abstract

A variety of simple aromatic compounds were identified in liquid cultures of the basidiomycetes Pleurotus cornucopiae, P. eryngii, P. floridanus, P. pulmonarius, P. ostreatus, and P. sajor-caju by using gas chromatography-mass spectrometry. Such compounds were detected in fungal cultures on lignin- and straw-containing media, but it was found that they were also produced in the absence of aromatic precursors. Anisylic and hydroxybenzylic compounds (such as alcohols, aldehydes, and acids) were identified, p-anisaldehyde being the most characteristic extracellular metabolite synthesized by these ligninolytic fungi. Small amounts of 3-chloro-p-anisaldehyde were also detected in several species. It is postulated that the balance between the more-or-less-oxidized aromatic compounds can be explained in terms of the activity of fungal enzymes, including aryl-alcohol oxidase and dehydrogenase. The former enzyme shows high affinity for p-anisyl alcohol, which is oxidized to p-anisaldehyde with production of H2O2. The aryl-alcohol dehydrogenase was detected only in the mycelium, where it reduces aromatic aldehydes in the presence of NADPH. Both enzymes could be involved in the redox cycling of these aromatic compounds, providing H2O2 to ligninolytic peroxidases.